Unlike existing 2D images, a 3D stereoscopic image is an image of a novel concept which is virtually similar to an actual image experienced by human beings, improving the quality level of visual information by a dimension. In general, the reason why human beings feel a 3D effect is because the right-eye and the left-eye recognize an object with a time difference. Namely, because the eyes of human beings are positioned to be spaced apart by an interval of approximately 65 mm, they see images in slightly different directions, thus achieving a 3D effect due to binocular disparity (or parallax). Namely, a 3D image effect can be implemented by inputting an image having a time difference to both of the eyes of a viewer.
The related art stereoscopic display device may be divided into a stereoscopic display device using 3D glasses and a stereoscopic display device not using 3D glasses. The stereoscopic display device using 3D glasses is devised to display a left-eye image and a right-eye image each having different polarization characteristics, and a polarizer or the like is attached to 3D glasses to allow only a left-eye image to be projected onto a left-eye lens and only a right-eye image to be projected onto a right-eye lens, thus allowing the user to experience a 3D effect. The 3D glasses scheme is disadvantageous in that the user must wear glasses, but advantageous in that restrictions on a viewing angle can be reduced and fabrication can be facilitated.
In general, the related art stereoscopic display device using 3D glasses includes a display panel for producing left-eye image light and right-eye image light and an optical filter attached to the display panel to change a polarization state of the left-eye image light and right-eye image light so as to have mutually different polarized states.
In this case, the optical filter is formed to have alternately patterned first and second areas and, in this case, the first area adjusts a polarized state of the right-eye image light and the second area adjusts a polarized state of the left-eye image light. In general, the first and second areas have the same phase difference values and phase difference layers whose optical axes are perpendicular to each other; for example, a −λ/4 phase difference layer and +λ/4 phase difference layer may be alternately arranged in stripes or in a checkerboard pattern.
The optical filter including alternately patterned first and second areas may be fabricated by coating photoresist on a substrate (or a base member), exposing a predetermined portion thereof, and processing the resultant structure with a potassium hydroxide solution to allow a certain portion to lose a phase difference delay function.
However, this method has a problem in that a complicated fabrication process must be performed due to chemical etching, resultantly increasing manufacturing costs and lowering productivity.
Another method for fabricating an optical filter is forming a phase difference layer by coating liquid crystal on a substrate or attaching a polymer stretched film or the like onto the substrate and removing a portion of the phase difference layer by laser, a grinder, or the like. However, this method has a problem in that it is difficult to obtain precise patterning and the phase difference layer may be damaged by laser, etching or the like, resulting in a defective optical filter.
In addition, with these methods, it is not easy to fabricate the optical filter such that the patterns of the optical filter are precisely matched to pixels of the display panel and the discrepancy between the patterns of the optical filter and the pixels of the display panel causes a high crosstalk rate.
In an effort to solve such problems, a method for fabricating an optical filter for a stereoscopic display device by printing a liquid crystal material for the formation of an alignment layer and/or a phase difference layer only on one of first and second areas of a substrate has been proposed. This method is advantageous in that pixels of a display panel and patterns of the optical filter are highly matched. However, in this method, the optical filter is fabricated such that a portion in which a liquid crystal layer is aligned (hereinafter, referred to as an ‘aligned portion’) and a portion in which a liquid crystal layer is not aligned (hereinafter, referred to as a ‘non-aligned portion’) are alternately arranged, and in this case, the optical performance of the non-aligned portion is considerably lower than that of the aligned portion, degrading the picture quality of an image display device overall.
Thus, in order to solve the problem, a method for forming an optical alignment layer on a substrate, performing primary alignment by irradiating UV polarized light, performing secondary alignment by irradiating UV polarized light perpendicular to the primarily irradiated UV polarized light only to a partial area by using a mask, and coating a liquid crystal layer thereon has been proposed. This method advantageously eliminates the presence of a non-aligned liquid crystal layer, but is disadvantageous in that the use of a mask makes the process complicated, and because the intensities of UV light irradiated onto the secondarily aligned area and the primarily aligned area are different, the liquid crystal alignment degree by the primarily aligned alignment layer and that by the secondarily aligned alignment layer are not uniform, resulting in a phase difference deviation. The phase difference deviation restrains a left-eye image and a right-eye image from being clearly separated and produces crosstalk, therefore failing to implement a sharp stereoscopic image.